Chaya, Rivka, Shifre, and Esther were talking about life before the Nazis took them when a new guard comes to take those who weren't working.
The guard decides to take away Esther and Shifre. For the third person, he points at Rivka and chooses her. Hannah realizes how important Rivka is to her.
After the guard leaves, Chaya takes the kercheif off of Rivka's head and ties it on her own. She is sacrificing her life for Rivka. She will be taken instead. Rivka has helped her many times, and Chaya wanted to her to be the one who lived